Method and system for measuring water hardness

ABSTRACT

Prior to adding detergent or chelant, the conductivity of water in a washing chamber is measured. The maximum concentration of hard water ions that could correspond to the measured conductivity is determined, i.e., it is assumed that all of the conductivity is from calcium and/or magnesium ions in the water even though other ions may in fact be contributing to the measured conductivity. Enough chelating agent is added to the chamber to sequester this maximum concentration of hard water ions and the conductivity is measured again. Using the two conductivity measurements, the actual concentration of hard water ions is determined. A chelant factor based on the actual concentration of hard water ions is then used to determine the amount of chelant to be added for subsequent wash cycles to sequester all of the hard water ions.

RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 11/090,344, filed Mar. 24, 2005 now U.S. Pat. No. 7,709,265, entitled “Method and System for Measuring Water Hardness,” which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present invention relates generally to measuring water hardness, and in particular to measuring, and compensating for, water hardness in a washing machine.

BACKGROUND

Machine washing systems typically employ cleaning agents that form a cleaning solution when mixed with water. Cleaning agents, such as detergents, breakdown and remove food or other soils and operate most effectively in alkaline environments. However, hard water ions (e.g., calcium and magnesium ions) present in the water supply of the washer will reduce the effectiveness of the detergent. Thus, chelating agents are added to the wash water to sequester the hard water ions. Typical chelants include, without limitation, nitrilotriacetic acid (NTA), ethylene diamene tetraacetic acid (EDTA) and tripolyphosphate (TPP).

The water hardness (i.e., the concentration of hard water ions) is typically not known prior to beginning a wash operation, so the amount of chelant that needs to be added to the wash water to sequester the hard water ions is also not known.

One approach to account for unknown water hardness is to add an excess amount of chelating agent to the detergent to sequester all possible hard water ions. However, this approach typically wastes a large amount of chelant. In addition, this approach is costly because chelating agents are expensive.

Two approaches to determining when enough chelant has been added to completely sequester the hard water ions are described in U.S. Pat. No. 4,334,881, entitled “Method and Apparatus for Automatic End-Point Detection in Tripolyphosphate Sequestration of Hardness.” In one approach, TPP is slowly added to the wash water while the electrical conductivity of the wash water is monitored. Complete sequestration is determined by detecting when the maximum rate of change of conductivity with chelant addition occurs. In the second approach, if the pH of the washing solution is above 11 (to precipitate the magnesium ions), when the conductivity first increases substantially with TPP addition, 1.5 times more TPP is added to sequester all of the remaining calcium ions. Both of these approaches, however, tend to be quite slow and inaccurate.

Thus, there is a need for improved methods and systems to measure water hardness and to determine the amount of chelating agent needed to sequester hard water ions.

SUMMARY

The present invention overcomes the limitations and disadvantages described above by providing methods and systems to measure water hardness and to determine and dispense the amount of chelating agent needed to sequester the hard water ions.

In one embodiment, a method for dispensing a chelant and a cleaning agent includes obtaining a first conductivity measurement and determining a first chelant amount based on the first conductivity measurement. The first chelant amount is added to a chamber from a chelant source and a second conductivity measurement is obtained. Based on the second conductivity measurement, a chelant factor is determined and stored. An amount of detergent is added to the chamber from a detergent source.

In another embodiment, a method for detecting a change in water hardness includes obtaining a first conductivity measurement and determining a first chelant amount based on the first conductivity measurement. The first chelant amount is added to a chamber from a chelant source and a second conductivity measurement is obtained. Based on the second conductivity measurement, a current chelant factor is determined. A change in the water hardness is based on comparing the current chelant factor and a previous chelant factor.

In still another embodiment, a method for detecting a change in water hardness includes adding chelant during each of a plurality of processing cycles to a chamber to sequester water hardness ions. A respective chelant factor is determined, where the chelant factor is related to water hardness for the respective processing cycle. The respective chelant factor for a current processing cycle is compared with at least one earlier determined chelant factor. When the comparing indicates a change in water hardness satisfying predefined criteria, a signal is generated.

In still another embodiment, a method for identifying a decrease in water softening effectiveness includes obtaining a first conductivity measurement and determining a first chelant amount based on the first conductivity measurement. A first portion of the first chelant amount is added to a chamber from a chelant source and a second conductivity measurement is obtained. An effectiveness of water softening is determined and a second portion of the first chelant amount is added to the chamber from the chelant source based on the effectiveness. A third conductivity measurement is obtained and a chelant factor based on the third conductivity measurement is determined and stored.

The value in knowing the water hardness is related to the potential to eliminate problems caused by uncontrolled water hardness and to reduce overuse of chelants. Water hardness can change for a variety of reasons, including changes in water supply sources, seasonal changes in aquifers, and water softener failures. This invention makes it is possible to easily detect these changes and to adjust the chelant accordingly, thereby saving chemical costs and improving wash results.

BRIEF DESCRIPTION OF THE DRAWINGS

The aforementioned embodiments of the invention, as well as additional aspects and embodiments thereof will be more clearly understood hereinafter as a result of a detailed description of embodiments of the invention when taken in conjunction with the drawings. Like reference numerals refer to corresponding parts throughout the several views of the drawings.

FIG. 1 is a schematic diagram illustrating an exemplary washing system according to an embodiment of the invention.

FIG. 2 is a block diagram illustrating a control system according to an embodiment of the invention.

FIG. 3 is a flow chart of an exemplary process for measuring water hardness and dispensing a chelant and a cleaning agent according to an embodiment of the invention.

FIGS. 4A and 4B are schematic graphs of electrical conductivity versus hard water ion concentration and electrical conductivity versus amount or concentration of chelating agent, respectively.

FIG. 5 is a flow chart of an exemplary process for measuring water hardness, dispensing a chelant and a cleaning agent, and identifying a decrease in water softening effectiveness according to an embodiment of the invention.

DESCRIPTION OF EMBODIMENTS

Water hardness is measured in a novel manner using an electrical conductivity sensor, one or more chelating agents, and a computer-controlled chemical dispensing system.

In some embodiments, an initial conductivity measurement of water in a washing chamber is made when a new fill cycle is detected. The maximum concentration of hard water ions that could correspond to the measured conductivity is determined, i.e., it is assumed that all of the conductivity is due to calcium and/or magnesium ions in the water even though other ions may in fact be contributing to the measured conductivity. Enough chelating agent is then added to the chamber to sequester this maximum concentration of hard water ions and the conductivity is measured again. Using the two conductivity measurements, the actual concentration of hard water ions is determined. A chelant factor based on the actual concentration of hard water ions is then used to determine the amount of chelant to be added for each subsequent wash cycle to sequester all of the hard water ions.

Methods, systems, and computer programs are described that measure water hardness and that determine and dispense the amount of chelating agent needed to sequester hard water ions. Reference will be made to certain embodiments of the invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the embodiments, it will be understood that it is not intended to limit the invention to these particular embodiments alone. On the contrary, the invention is intended to cover alternatives, modifications and equivalents that are within the spirit and scope of the invention as defined by the appended claims.

Moreover, in the following description, numerous specific details are set forth to provide a thorough understanding of the present invention. However, it will be apparent to one of ordinary skill in the art that the invention may be practiced without these particular details. In other instances, methods, procedures, and components that are well known to those of ordinary skill in the art are not described in detail to avoid obscuring aspects of the present invention.

FIG. 1 is a schematic diagram illustrating an exemplary washing system according to an embodiment of the invention. Washing system 100 includes a washing chamber 102, a control system 104, a cleaning agent dispenser 106, a chelant dispenser 108, and a water supply 110. In some embodiments, washing system 100 is a commercial dishwasher. In other embodiments, washing system 100 is a consumer dishwasher, a commercial clothes washer, or a consumer clothes washer.

Washing chamber 102 is a connected to a drain 112.

Control system 104 is connected to meter 114, conductivity sensor 118, cleaning agent dispenser 106 and chelant dispenser 108. Meter 114 monitors the flow of water from water supply 110 into washing chamber 102.

Conductivity sensor 118 can be a typical sensor that is normally used to measure the detergent concentration in a commercial dishwasher. Details on this type of sensor and the electronics and control associated with it are described in U.S. Pat. Nos. 6,223,129 and 6,529,841, the contents of which are hereby incorporated by reference. Other types of conductivity measurement systems will also work. Conductivity sensor 118 may also include a temperature sensor so that raw conductivity measurements can be compensated back to 20° C. using the standard 1.8%/° C. compensation factor.

Dispensers 106 and 108 are similar to those used to dispense chemicals into a commercial dishwasher. Exemplary dispensers are described in U.S. Pat. No. 5,647,391, the contents of which are hereby incorporated by reference. The chemical forms of the cleaning agent and the chelant may be either liquid or solid (powder). Control system 104 should be capable of controlling the addition of the chemicals in accurate dose amounts. Typical dose amounts are between 5 cc's (or 5 grams) and 250 cc's (or 250 grams). Typical accuracy should be +/−5% of the target dose amount, or +/−1 cc, or +1-1 gram). These numbers and accuracies are for typical commercial dishwashers and should not be considered as limits on the scope of the invention.

The chemicals serve two purposes. Their primary role is to support the cleaning process of the dishwasher. Their secondary role is as reagents for water hardness measurements. In some embodiments, the detergent is split into two separate chemicals; one contains the primary cleaning ingredients and the other contains the chelant. The chelant is used to control (sequester) the hard water ions. To create a complete detergent, the cleaning chemical, often called the “chemical energy” or “CE” component, is added to the wash tank to a concentration level determined by the soil levels that will be present (less if light soil is most probable and more if heavy soil is more likely). The chelant, often called the “chelation value” or “CV” component, is added to a concentration level that will sequester all of the hardness ions. Since the CV component is quite costly, it is most cost effective to not dose more chelant than is required.

FIG. 2 is a block diagram illustrating a control system according to an embodiment of the invention. Control system 104 typically includes processing unit (CPU) 222, one or more network or other communications interfaces 232, memory 202, and one or more communication buses 224 for interconnecting these components. Control system 104 optionally may include a user interface 116 comprising a display device 228 and a keyboard 230. Memory 202 may include high speed random access memory and may also include non-volatile memory, such as one or more magnetic disk storage devices. Memory 202 may optionally include one or more storage devices remotely located from the CPU 222. In some embodiments, the memory 202 stores the following programs, modules and data structures, or a subset thereof:

-   -   an operating system 204 that includes procedures for handling         various basic system services and for performing hardware         dependent tasks;     -   a communication module 206 that is used for connecting control         system 104 to other computers (e.g., for remote monitoring of         washing system 100) or devices via one or more communication         interfaces 232 (wired or wireless); the communication interfaces         may include a network interface (for connecting to the Internet,         a local area network, or the like), an RS232 interface, or any         other suitable interface;     -   a water control module 208 that regulates the amount of water in         chamber 102;     -   a chelant control module 210 that regulates the amount of         chelant added to chamber 102 by dispenser 108;     -   a detergent control module 212 that regulates the amount of         cleaning agent added to chamber 102 by dispenser 106;     -   a conductivity sensor module 214 that controls or monitors the         operation of sensor 118;     -   a hardness calculation module 216 that determines hard water ion         concentrations and chelant dose amounts based at least in part         on conductivity measurements and water volume;     -   a comparison module 218 that compares current hard water ion         concentrations and/or chelant factors with previous values to         identify changes in water hardness and/or water softener         effectiveness; and     -   a wash module 220 that controls the washing process in chamber         102.

Each of the above identified modules corresponds to a set of instructions for performing a function described above. These modules (i.e., sets of instructions) need not be implemented as separate software programs, procedures or modules, and thus various subsets of these modules may be combined or otherwise re-arranged in various embodiments. In some embodiments, memory 202 may store a subset of the modules and data structures identified above. Furthermore, memory 202 may store additional modules and data structures not described above.

FIG. 3 is a flow chart of an exemplary process for measuring water hardness and dispensing a chelant and a cleaning agent according to an embodiment of the invention.

Control system 104 determines if a new fill cycle for washing system 100 has occurred (302). In a new fill cycle, chamber 102 is filled with clean water from supply 110 prior to the start of washing. Various methods can be used to sense when chamber 110 has been drained and refilled with clean water. U.S. Pat. No. 4,509,543 describes a method that uses a conductivity sensor, such as sensor 118. Alternatively, a float switch could be used to sense a tank drain and refill. If a new fill cycle has occurred, a first conductivity measurement of the (clean) water is obtained (304), for example by conductivity sensor module 214 using sensor 118.

The first conductivity measurement is converted to a maximum hard water ion concentration (306). In some embodiments, hardness calculation module 216 uses an equation or lookup table relating conductivity to hard water ion concentration to make the conversion. FIG. 4A is a schematic graph of electrical conductivity versus hard water ion concentration at a particular temperature. The data for such a graph (and the corresponding equations or lookup table) can be obtained by measuring the conductivity of initially pure water samples as known amounts of hard water ions are added. These measurements can also be done at a series of temperatures so that the temperature dependence of the conductivity can be accounted for. Thus, a first conductivity measurement (e.g., A in FIG. 4A) can be converted to a maximum possible hard water ion concentration (e.g., B in FIG. 4A). Hard water ion concentrations are typically expressed in ppm (parts per million) of calcium ions.

Based on the first conductivity measurement, an amount of chelant to be added to the water in chamber 102 is determined (308). In some embodiments, the chelant amount is an amount that is projected to be sufficient to fully sequester water hardness ions in the chamber. For example, if a 1:1 molar ratio of chelant to hard water ions is needed to fully sequester the hard water ions, then the amount of chelant needed is given by Chelant volume=(maximum possible hard water ion concentration)·(volume of water in chamber)

The amount of chelant needed can also be expressed as a mass by multiplying the preceding equation by the appropriate density.

In some embodiments, hardness calculation module 216 calculates the chelant amount required based on the maximum possible hard water ion concentration (derived from the first conductivity measurement) and the amount of water that meter 114 determines has gone into chamber 102 during the new fill cycle.

The calculated chelant amount is added to chamber 102 from chelant source 108 (310). The chelant can be added with a peristaltic metering pump (or any other suitable liquid pump) if the chelant is a liquid or with a powder measuring device (also called a powder metering device) if the chelant is a powder. After the chelant is thoroughly mixed with the water in chamber 102, a second conductivity measurement is obtained (312). Complete mixing can be sensed by monitoring for stability in the conductivity measurement. Alternately, the system can wait a predefined amount of time after the dispensing operation to perform the second conductivity measurement.

Based on the second conductivity measurement, the actual hard water ion concentration is determined (314). This determination can be explained with the aid of FIG. 4B, which is a schematic graph of electrical conductivity versus the amount of chelating agent added for three different water samples with the same initial conductivity (A in FIG. 4B), but different actual hard water ion concentrations.

As shown in U.S. Pat. No. 4,334,881, the conductivity increases slowly with added chelant until the hard water ions are fully sequestered. Full sequestration typically occurs at a 1:1 molar ratio of hard water ions to chelant elements. Once the hard water ions are fully sequestered, the conductivity rises more rapidly with additional chelant, at about the same rate as would occur in water containing no hard water ions. This behavior explains the change in slope in lines 402 and 404. The slope after complete sequestration may depend on which chelant is being added. This slope may be determined by adding chelant to pure water samples and measuring the change in conductivity.

Line 404 shows schematically the conductivity behavior for a water sample where the actual hard water ion concentration is the concentration derived from the first conductivity measurement (i.e., B derived from A in FIG. 4A). In other words, for this sample, the assumption that essentially all of the conductivity is due to hard water ions is correct. Consequently, for this sample, the amount of chelating agent added (C in FIG. 4B) is just enough to fully sequester the hard water ions; the second conductivity measured is D in FIG. 4B; and no excess chelant is wasted.

Line 400 shows schematically the conductivity behavior expected for a water sample where the hard water ion concentration is negligible. In other words, for this sample, all of the conductivity is due to ions other than hard water ions. For this sample, no chelating agent is needed because there are no hard water ions to sequester. Consequently, there is no slow increase in conductivity for this sample. Instead, the conductivity rises rapidly as soon as chelant is added to the water, ending up at F in FIG. 4B when the amount of chelant added is C.

Line 402 shows schematically the conductivity behavior expected for a water sample where the hard water ion concentration is not negligible, but is less than the concentration derived from the first conductivity measurement. In other words, for this sample, only part of the conductivity is due to hard water ions. For this sample, the amount of chelating agent needed to sequester the hard water ions is G in FIG. 4B. When the amount of chelant added to this sample is C, then some chelating agent (i.e., C-G in FIG. 4B) is wasted and the second measured conductivity is E in FIG. 4B.

The second conductivity measured for samples with only a portion of the conductivity due to hard water ions varies in an approximately linear manner between F (no conductivity due to hard water ions) and D (all conductivity due to hard water ions) in FIG. 4B. Thus, if the slopes before and after complete sequestration are known for a given chelating agent (e.g., from prior conductivity measurements on water samples with controlled chelant concentrations) and the conductivities before and after addition of the chelating agent are measured, the second conductivity measurement can be converted to the actual hard water ion concentration. In some embodiments, the conductivity versus amount of chelant slopes before and after complete sequestration are stored for one, or two or more chelants in memory 202 and used by hardness calculation module 216 to convert the second measured conductivity to an actual hard water ion concentration.

In one embodiment, conductivity measurements were made at 20° C., resulting in the determination of the following first-order relationships:

In FIG. 4A: B=1.14×A

where

-   -   A=clean water conductivity, in uS/cm, and     -   B=maximum possible hard water ion concentration, ppm calcium         ions.

In FIG. 4B: D=1.25×A and F=(1.65×A)+304 uS/cm

-   -   where     -   A=the clean water conductivity, in uS/cm,     -   D=the conductivity measured after an amount of chelant C is         added and mixed when all of the initial conductivity was due to         hard water ions, and     -   F=the conductivity measured after an amount of chelant C is         added and mixed when none of the initial conductivity was due to         hard water ions.

These equations, in conjunction with the two conductivity measurements (i.e., the clean water conductivity and the conductivity measured after the chelant is added and mixed) can also be used to calculate the actual hard water ion concentration.

In some embodiments, tables are used, rather than equations, to calculate the actual hard water ion concentration. In the tables, for each starting conductivity (interpolation can be used to keep the table size reasonable), there is an array of possible ending conductivities that relate to the percentage of the maximum possible hard water ion concentration. The range would extend from 100% to 0%. In other words, while the maximum possible hard water ion concentration may have been 700 ppm, the second conductivity measurement may indicate that only 30% of the ions were hard water ions and that the actual hard water ion concentration is only 210 ppm. Table 1 is an exemplary table.

TABLE 1 Table for converting conductivity after chelant addition to hard water ion concentration for a starting conductivity of 600 uS/cm, at 20° C. Ending Conduc- Percent of maximum possible Actual hard water ion tivity, uS/cm hard water ion concentration concentration, ppm 760 100 700 898 75 525 1036 50 350 1173 25 175 1310 0 0

In some embodiments, the actual hard water ion concentration can be compared to previous measurements to detect a significant change in the hard water ion concentration (316), for example by using comparison module 218. More specifically, the actual hard water ion concentration determined at each refilling of the water tank may be compared with one or more previously hard water ion concentrations determined at prior refillings of the water tank. Alternately, the current hard water ion concentration determination may be compared with an average of two or more previously hard water ion concentrations. A significant change in the hard water ion concentration determination (e.g., an increase of N percent, such as 20 percent, or an increase of a predefined amount, such as 150 ppm) may indicate a failure of a water softener device, or may indicate another condition or problem requiring the attention of a repair person. When the comparison at 316 indicates that the current hard water ion concentration is significantly higher than prior hard water ion concentration determinations, a remedial action maybe initiated. The remedial action may include turning on a warning light, sending a message to another device or to a particular email address or the like, or other appropriate action. In one embodiment, the remedial action is undertaken only when the new, higher hard water ion concentration determination is confirmed during a subsequent refilling of the water tank.

In some embodiments, the change in water hardness at 316 is detected by comparing a chelant factor computed (318) for a current water fill cycle with the chelant factor computed for one or more prior water fill cycles, and determining whether the difference (if any) exceeds a predefined threshold. In these embodiments, and in some other embodiments as well, detection operation 316 occurs after the calculation of the chelant factor at 318.

An amount of chelant needed to sequester the actual hard water ion concentration is calculated (318). In some embodiments, this calculation uses a chelant factor. As used herein, a chelant factor is a multiplier used in the calculation of the amount of chelant needed for sequestration that compensates for the fact that only a portion of the measured conductivity may be due to hard water ions. The chelant factor incorporates or corresponds to the fraction of the water conductivity that is actually due to hard water ions. If a 1:1 molar ratio of chelant to hard water ions is needed to fully sequester the hard water ions, then the amount of chelant needed when additional water is added to chamber 102 is given by: Chelant volume=(chelant factor)(maximum possible hard water ion concentration)(incremental volume of water added to chamber)

If a molar ratio other than 1:1 is needed for a particular chelant to fully sequester the hard water ions, this ratio can be incorporated into the chelant factor. More generally, the chelant factor is a multiplier for determining the amount of chelant (by volume or weight) needed to fully sequester the hard water ions based on a conductivity measurement and the incremental amount of water. Thus, in some embodiments, the chelant factor may also incorporate a conversion factor that relates a measured conductivity to a maximum possible hard water ion concentration.

For line 402 in FIG. 4B, the chelant factor is G/C or, equivalently, (F−E)/(F−D). The chelant factor, which is based on the second conductivity measurement, the first conductivity measurement, and the conductivity slopes before and after complete sequestration, is determined and stored in memory 202 (e.g., by hardness calculation module 216).

An amount of detergent is added (320) to chamber 102 from a detergent source, such as cleaning agent dispenser 106, and washing (322) is performed by washing system 100.

In some embodiments, such as commercial washing machines, chamber 102 is not completely drained and refilled with water between each wash cycle. Instead, an incremental amount of water is added to chamber 102 that, in turn, needs an incremental amount of chelating agent and detergent added as well. In such cases, control system 104 determines that there is not a new fill cycle (302).

The incremental amount of water added from water supply 110 to chamber 102 is determined, for example using meter 114. A second chelant amount in accordance with the amount of added water and the chelant factor is determined using the equation given above. The second chelant amount is added to chamber 102 from chelant source 108 (324).

In addition, an incremental amount of detergent is added (320) to chamber 102 from a detergent source, such as cleaning agent dispenser 106, and additional washing (322) is performed by washing system 100.

In some embodiments, with each new fill cycle, a current chelant factor is determined based on a second conductivity measurement, a first conductivity measurement, and the conductivity slopes before and after complete sequestration, using the process described above. A change in water hardness is determined based on the current chelant factor and a previous chelant factor. An increase in water hardness is identified when the current chelant factor is greater than the previous chelant factor.

In some embodiments, during each of a plurality of processing cycles, chelant is added to a chamber to sequester water hardness ions and a chelant factor is determined for each processing cycle using the process described above. As explained above, each chelant factor relates to the water hardness for the respective processing cycle. The chelant factor for a current processing cycle is compared with at least one earlier determined chelant factor. When the comparison indicates a change in water hardness satisfying some predefined criteria, a signal such as a visual and/or auditory alarm, or an electronic message transmitted to another device, is generated. In some embodiments, the predefined criteria include the change in chelant factor being greater than a predefined amount.

The water hardness measurement processes described above are based on adding an amount of chelant equal to the maximum that could possibly be required (308 and 310). In most cases, this will not cause a large waste of chelant because it is only done once for each tank drain and fill cycle and because the ions in the clean water will typically be mostly hard water ions. However, an exception to the typical case occurs when an ion exchange water softener is used. When the water softener is working properly, most of the ions will be sodium and not require sequestering. As described below with respect to FIG. 5, control system 104 and the hardness measurement process can be made to detect that a softener is employed. If softener use is detected, then control system 104 adds only a fraction of the calculated maximum chelant dose (308/508). If the conductivity rises at a rate that indicates the softener is working, then no more chelant is added. If the conductivity rises slowly with chelant, indicating at least moderate hardness, then the rest of the chelant dose is added and the normal hardness measurement is performed. In some embodiments, control system 104 detects that a softener is in use if the percentage of actual hardness calculated in the normal measurement is less than 25% of the potential maximum hard water ion concentration. This embodiment could also be useful in cases where there is a natural occurrence of non-hard water ions with few hard water ions present.

FIG. 5 is a flow chart of an exemplary process for measuring water hardness, dispensing a chelant and a cleaning agent, and identifying a decrease in water softening effectiveness according to an embodiment of the invention. This process builds on the exemplary process shown in FIG. 3 and discussed above, so analogous steps or operations that are already explained in detail above will only be briefly discussed here.

Control system 104 determines if a new fill cycle for washing system 100 has occurred (502). If so, a first conductivity measurement of the wash water is obtained (504). The first conductivity measurement is converted to a maximum hard water ion concentration (506). Based on the first conductivity measurement, an amount of chelant to be added to the water in chamber 102 is determined (508). In some embodiments, the chelant amount is an amount that is projected to be sufficient to fully sequester water hardness ions in the chamber.

Control system 104 determines if a softener is present (526). In some embodiments, this determination can be made based on a previous measurement of water hardness finding less than a predetermined amount of the conductivity due to hard water ions (e.g., less than 25%). In some embodiments, this determination can be made based on user input (e.g., a flag or other value may be stored in the control system 104 based on a user input to the control system).

If softener is known or believed to be present, just a portion of the calculated maximum chelant dose is added to chamber 102 (528) from chelant dispenser 108. After thoroughly mixing the added chelant, a second conductivity measurement is obtained (530). In some embodiments, the amount of chelant added at 528 is sufficient to distinguish between water having a low, expected concentration of hard water ions (e.g., a concentration similar to what was determined during one or more previous water cycles, or a predetermined concentration consistent with the use of a water softener) and water having an unexpectedly high concentration of hard water ions. This amount of chelant will typically be much less (e.g., at least 50 percent less) than the amount of chelant that would be required if all the ions contributing to the measured conductivity were attributable to hard water ions.

In some embodiments, the effectiveness of the water softening is determined as follows. If the added chelant creates a rapid rise in conductivity, the softener is working properly (532) and no more chelant needs to be added. The detergent is added (520) and washing begins (522).

Conversely, if the added chelant creates a slow rise in conductivity, the softening is not effective (532) and a second portion of the maximum chelant dose is added to chamber 102 (534). In some embodiments, the second portion equals the maximum chelant dose less the first chelant portion (i.e., the second portion is the remaining amount of the maximum chelant dose). After thoroughly mixing the added chelant, a third conductivity measurement is made (512) and the actual hard water ion concentration is determined (514). In some embodiments, control system 104 detects that a softener is in use if the percentage of actual hardness calculated in the normal measurement is less than a predetermined amount (e.g., less than 25%) of the maximum possible hard water ion concentration (516). An amount of chelant needed to sequester the actual hard water ion concentration is calculated (518). As explained above, this calculation uses a chelant factor in some embodiments. The chelant factor based on the third conductivity measurement is determined (e.g., by hardness calculation module 216) and stored (e.g., in memory 202). The detergent is added (520) and washing begins (522).

If softener is not known or believed to be present (526), the calculated maximum chelant dose is added to chamber 102 (510). After thoroughly mixing the added chelant, a conductivity measurement is made (512) and the actual hard water ion concentration is determined (514). In some embodiments, control system 104 detects that a softener is in use if the percentage of actual hardness calculated in the normal measurement is less than a predetermined amount (e.g., less than 25%) of the maximum possible hard water ion concentration (516). An amount of chelant needed to sequester the actual hard water ion concentration is calculated (518). As explained above, this calculation uses a chelant factor in some embodiments. The detergent is added (520) and washing begins (522).

If this is not a new fill cycle (502), an incremental amount of water is added to chamber 102 that, in turn, needs an incremental amount of chelating agent and detergent added as well. The incremental amount of water added from water supply 110 to chamber 102 is determined, for example using meter 114. A second chelant amount in accordance with the amount of added water and the chelant factor is determined using the equation given above. The second chelant amount is added to chamber 102 from chelant source 108 (524). An amount of detergent is added (520) to chamber 102 from a detergent source and washing (522) is performed by washing system 100.

In addition to detecting and compensating for a failed water softener, control system 104 can also warn the user that it is time to recharge the water softener. Control system 104 can automatically increase the chelant feed from dispenser 108 while the softener is “leaking hard water” and then decrease it when the softener system or device has been serviced and restored to normal operation.

In some embodiments, the determinations at 526 and 516 may also be used to detect the presence of soft water, with low hard water ion concentrations, even when a softener system is not in use. By detecting that the washing system is receiving soft water, the amount of chelant used at the beginning of each fill cycle may be significantly reduced (e.g., by 50 percent or more).

In some embodiments, to reduce the amount of chelant wasted by repeated determinations of the chelant factor, a new chelant factor determination is performed only once every N fill cycles, where N is equal to 2, 3, 4 or other larger number. In some other embodiments, when the chelant factor is below a threshold value (e.g., below a value corresponding to 50% of the ions comprising hard water ions), the chelant factor is assumed to be correct from one fill cycle to the next, but is tested at the beginning of each new fill cycle, or each Nth new fill cycle. The chelant factor is tested or checked by adding an amount of chelant that falls between a low value corresponding to the previously determined chelant factor and a high value corresponding to the amount of chelant that would be needed if all the ions associated with the current conductivity measurement were hard water ions, and then taking a new conductivity measurement, computing a new chelant factor and comparing the new chelant factor with the previously computed chelant factor. By using less chelant than the aforementioned high value, the total amount of chelant used is reduced. In all of these embodiments, a single chelant dispensing event or operation is used for each wash cycle, except in the rare situations in which a water softener system has failed or a significant change in water hardness is detected.

Although some of various drawings illustrate a number of logical stages in a particular order, stages which are not order dependent may be reordered and other stages may be combined or broken out. While some reordering or other groupings are specifically mentioned, others will be obvious to those of ordinary skill in the art and so do not present an exhaustive list of alternatives. Moreover, it should be recognized that the control system could be implemented in hardware, firmware, software or any combination thereof.

The foregoing description, for purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. 

1. A method for detecting a change in water hardness, comprising: during each of a plurality of processing cycles, adding chelant to a chamber to sequester hard water ions and measuring water conductivity to determine a respective chelant factor, wherein the chelant factor corresponds to a fraction of water conductivity due to hard water ions for the respective processing cycle; comparing the respective chelant factor for a current processing cycle with at least one earlier determined chelant factor; and when the comparing indicates a change in water hardness satisfying predefined criteria, generating a signal.
 2. The method of claim 1, wherein the predefined criteria include the change being greater than a predefined amount.
 3. The method of claim 1, including determining the respective chelant factor by: obtaining a first conductivity measurement; determining a first chelant amount based on the first conductivity measurement; adding the first chelant amount to a chamber from a chelant source; obtaining a second conductivity measurement after adding the first chelant amount to the chamber; and computing the respective chelant factor based on a plurality of values, including the first conductivity measurement, the second conductivity measurement, and the first chelant amount, wherein the respective chelant factor corresponds to a fraction of water conductivity due to hard water ions.
 4. The method of claim 3, including determining as the first chelant amount an amount of chelant that is projected to be sufficient to fully sequester hard water ions in the chamber.
 5. The method of claim 3, including identifying an increase in water hardness when the respective chelant factor is greater than a previous chelant factor.
 6. The method of claim 3, wherein the plurality of values further includes a first predetermined conductivity slope, representing the rate of increase of conductivity as a chelant is added when there are non-sequestered hard water ions in the chamber; and wherein the plurality of values further includes a second predetermined conductivity slope, representing the rate of increase of conductivity as a chelant is added when there are no non-sequestered hard water ions in the chamber.
 7. The method of claim 1, including determining the respective chelant factor by: obtaining a first conductivity measurement; determining a first chelant amount based on the first conductivity measurement; adding a first portion of the first chelant amount to a chamber from a chelant source; obtaining a second conductivity measurement after adding the first portion of the first chelant amount to the chamber; determining an effectiveness of water softening; adding a second portion of the first chelant amount to the chamber from the chelant source based on the effectiveness; obtaining a third conductivity measurement after adding the second portion of the first chelant amount to the chamber; and determining the respective chelant factor based on a plurality of values, including the first conductivity measurement, the third conductivity measurement, and the first chelant amount, wherein the respective chelant factor corresponds to a fraction of water conductivity due to hard water ions.
 8. The method of claim 7, including determining as the first chelant amount an amount of chelant that is projected to be sufficient to fully sequester hard water ions in the chamber.
 9. The method of claim 7, wherein the second portion equals the first chelant amount less the first portion.
 10. The method of claim 7, wherein the plurality of values further includes a first predetermined conductivity slope, representing the rate of increase of conductivity as a chelant is added when there are non-sequestered hard water ions in the chamber; and wherein the plurality of values further includes a second predetermined conductivity slope, representing the rate of increase of conductivity as a chelant is added when there are no non-sequestered hard water ions in the chamber.
 11. A non-transitory computer readable storage medium storing one or more programs for execution by one or more processors of a computer system, the one or more computer programs comprising instructions for: adding chelant to a chamber during each of a plurality of processing cycles, in order to sequester hard water ions; and measuring water conductivity during each of the plurality of processing cycles to determine a respective chelant factor, wherein the respective chelant factor corresponds to a fraction of water conductivity due to hard water ions for the respective processing cycle; comparing the respective chelant factor for a current processing cycle with at least one earlier determined chelant factor; and generating a signal when the comparison indicates a change in water hardness satisfying predefined criteria.
 12. The computer readable storage medium of claim 11, wherein the predefined criteria include the change being greater than a predefined amount.
 13. The computer readable storage medium of claim 11, including instructions for determining the respective chelant factor, the instructions for determining the respective chelant factor comprising instructions for: obtaining a first conductivity measurement; determining a first chelant amount based on the first conductivity measurement; adding the first chelant amount to a chamber from a chelant source; obtaining a second conductivity measurement after adding the first chelant amount to the chamber; and computing the respective chelant factor based on a plurality of values, including the first conductivity measurement, the second conductivity measurement, and the first chelant amount, wherein the respective chelant factor corresponds to a fraction of water conductivity due to hard water ions.
 14. The computer program product of claim 13, including instructions, which, when executed, determine as the first chelant amount an amount of chelant that is projected to be sufficient to fully sequester hard water ions in the chamber.
 15. The computer program product of claim 14, including instructions, which, when executed, determine an amount of water added to the chamber, instructions, which, when executed, determine a second chelant amount in accordance with the amount of added water and the chelant factor; and instructions, which, when executed, add the second chelant amount to the chamber.
 16. The computer program product of claim 15, including instructions, which, when executed, obtain a third conductivity measurement; and instructions, which, when executed, determine if water hardness has significantly increased, and when such determination is positive, initiate a remedial action. 